Linnean Society. 287 
of their growth, and scarcely even of vitality. Yet affixed by one 
extremity to the shell, and by the mouth to the skin of the cater- 
pillar, they grew rapidly until at from the 12th to the 15th day they 
had acquired their full size, and measured half an inch in length, and 
then for the first time became detached from the shell. The author 
then described the form and motions of the stomach as seen through 
the tegument on the second day of growth, and also the structure 
of the head, the distribution of the trachez, and the mode in which 
the larva changes its skin while still attached to the egg-shell: This 
change was now seen for the first time in the apodal larve of Hyme- 
noptera, as noticed in the first part of this paper, in these larvee of 
Paniscus. It occurred at least three times in each larva before 
quitting its shell. The skin is burst as in other insects along the 
dorsal surface of the thorax, and is gradually carried backwards 
chiefly by the effect of growth of the larva, but it continues to in- 
close the caudal segments, which are also included between the two 
halves of the shell. The fourth change occurs when the insect is 
transformed to a nymph. It assumes this state inclosed in a leather- 
like cocoon spun by itself after it has destroyed the caterpillar on 
which it has fed, and while lying in the earthen chamber which the 
caterpillar had formed for its own change under ground. The change 
to a nymph took place in April, and to the perfect Ichneumon fly, 
Paniscus virgatus, in May 1848. 
The author then describes the mode in which the alimentary canal 
is originally developed in the embryo of insects. The first developed 
portions of the embryo are, first, the ventral, and then the lateral 
parietes of the segments. The lateral grow from below upwards, 
until their free margins ultimately approach along the future dor- 
sal surface, meeting first of all in the cephalic, and then in the cau- 
dal segments. The termination of the future alimentary canal in 
the anal segment is the result of a fold on itself of a layer of the 
first portion of the yolk included by the completion of the two cau- 
dal segments, and is the commencement of the column of cells, 
which afterwards becoming perforated when the larva is full-grown, 
form the colon and intestine, and which retains the celliform struc- 
ture to so late a period in the larva of Monodontomerus. ‘The re- 
mains of the yolk are included within the body by the union of the 
segments along the dorsal surface, and form the digestive cavity, 
the last portion included being in the prothorax, at which point the 
yolk enters the body in Crustacea, as pointed out by Rathke. The 
mode in which the great digestive cavity, or stomach, and the dif- 
ferent structures of the canal are formed is then described, and the 
general configuration of the organ is shown to be very similar, during 
the earlier stages of growth, in all embryos of insects. ‘This pri- 
mary form is longer retained in the imperfect apodal larve, espe- 
cially inthe parasites, than in other species, and hence the incom- 
pleteness noticed in Monodontomerus. 'The structure is completed 
earlier in Microgaster and Ichneumon ; but although in these a true 
colon and intestine are formed, these continue closed, and no feces 
are passed until the larva is matured. The appendages of the canal 
follow the same laws of development. The glands which produce 
